The objective of this proposal is to assess the feasibility of using recombinant virus-like- particles (VLPs) to elicit neutralizing antibodies and prime CD4+ T cells reactive with hepatitis B viral (HBV) antigens as candidate immunotherapeutics for chronic HBV infection. For this purpose, we have defined 8 neutralizing B cell epitopes from the HBV envelope Pre-S1 region, which will be consolidated and inserted onto a species variant of the HBV core protein, namely the woodchuck hepatitis core antigen(WHcAg). Pre-S1 B cell epitopes were chosen because of their preferential expression on HBV virions. The WHO estimates that more than 360 million individuals are chronically infected with HBV and approximately 20- 40% will develop serious complication such as cirrhosis, liver failure and hepatocellular carcinoma. Although a safe and efficacious preventative vaccine for HBV has been available for over 20years, HBV infections continue (with more than 50 million HBV infections per year) to be a major health problem and no effective treatments for chronic infection exist. Antiviral drugs have improved the therapeutic options for chronic HBV, but, their efficacy remains limited due to reactivation of HBV replication upon drug withdrawal. Vaccine-based immunotherapy has been suggested as a possible monotherapy or as a combination therapy with antiviral drugs. However, immune tolerance has prevented therapeutic vaccine efficacy. To circumvent the obstacle of immune tolerance in HBV chronic carriers, we have chosen the WHcAg, which is approximately 66-68% homologous with the HBcAg, as a vaccine carrier. The WHcAg and the HBcAg are not crossreactive at the B cell level and, just as importantly for our purposes, are only partially crossreactive at the CD4+ T cel level. Therefore, CD4+ T cells specific for WHcAg-unique T cell sites will provide cognate T-B cell help for anti- PreS1 antibody production and will not be curtailed by immune tolerance. In fact, in preliminary studies in HBcAg-Tg mice, which are tolerant to HBcAg, immunization with hybrid WHcAg- PreS1 VLPs elicits equivalent high titer anti- PreS1 antibodies in wildtype and HBcAg-Tg mice. Specifically, in Aim 1 we propose to consolidate 8 HBsAg-PreS1 neutralizing B cell epitopes onto the WHcAg VLP carrier and optimize the constructs based on assembly, yield, stability and immunogenicity and the therapeutic efficacy of the VLP-based vaccine candidates will be evaluated in a transgenic (Tg) mouse model of HBV replication. In Aim 2 preclinical development of the WHcAg-PreS1 vaccine will be pursued including cGMP manufacturing and pharm/tox studies.